The invention relates to an apparatus for coating a viscous medium onto predetermined surface portions of a plurality of members each having an axis about which the members are symmetrical. Exemplary of such members are cylindrically shaped workpieces as, for example, screws, bolts and the like, the predetermined surface portions of which to be coated in the described embodiment, are threaded shank portions.
In the disclosure to follow, it is to be understood that when referring to cylindrically shaped workpieces, it is intended to encompass workpieces which may have essentially cylindrical bodies with either smooth or profiled peripheral surfaces, such, for example as peripheral threaded or knurled surfaces while at the same time having non-cylindrical portions such as the screw head portions of threaded members.
For securing threaded members, such as screws or nuts, against loosening, particularly under changing temperature, load, shock or vibratory conditions, it is known to use locking means such as lock washers, taper pins and even a coating material on the threaded portion of a screw, the coating material being a single or multi-component adhesive or hardenable liquid plastic which may be in micro-capsulated form. The present invention is concerned with (a) the use of a coating material on for example the thread portion of a screw member for ensuring secure, non-loosening threaded engagement with a complementary threaded member and (b) an apparatus for applying optimum, accurately determined, predetermined amounts of the coating material to the member to be coated.
Micro-encapsulation is accomplished by a physico-chemical process and involves encapsulation of miniscule amounts of fluids or solids as by coacervation. When the capsule is crushed, for example, by exertion of a predetermined pressure on the capsule, the encapsulated contents is released from the capsule. The size of the capsule, in the embodiment described, is a function of the pitch of the thread, taking into account design tolerances.
The microcapsules may be placed in a lacquerlike binder to provide a preparation having a viscosity of between 2000 and 5000 cp. Preferably, the microcapsules are uniformly distributed in the binder under action of agitator blades. A preparation suitable for coating cylindrical workpieces, comprising microcapsules in a liquid binder, is described in German publication 2,307,252.
Workpiece objects have been coated by different methods. For instance, externally dry microcapsules have been applied to objects provided with an adhesive or binder, microcapsulation application having been accomplished by dusting, dripping or other suitable means. Such methods, however, are inefficient since large quantities of coated screws cannot be produced using such coating techniques.
It has also been proposed to pass objects to be coated through an immersion bath containing a binder system and a lacquerlike liquid. This method, however, suffers from the inability to control coating thickness, area of application or operating speed.
Also known is a method suited for automated coating of objects, such method being described in German publication 2,307,238. The method described in this patent requires manifold stations in addition to a coating station to insure uniform coating application, especially due to release of the coating material through a zig-zag slot which is apt to release more coating material than required and to clog when operation is interrupted for a time during which the relatively viscous binder tends to solidify.
Moreover, with the method of this publication, because the viscous medium is squeezed out of the zig-zag slot under action of a pulsating pump, it is not possible to produce on the screw shank a coating of predetermined thickness. Furthermore, to vary the width of the coating to be applied, the coating device of this publication must be replaced because the width of the applied coating is a function of the width of the working area of the coating applicator. Hence, if the coating width is to be varied, the applicator head must be separated from the pump and exchanged.